TAP Controller Star Configuration Testing
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Solution Overview
Problem
Testing of complex electronic circuits in a star configuration is challenging due to drive conflicts on shared signal lines, as existing JTAG standards are designed for series configurations and cannot perform shift operations concurrently in a star setup.
Innovation Solution
A method and system that allow TAP controllers in a star configuration to perform capture and update phases concurrently, while sequentially selecting and shifting data from each controller to avoid drive conflicts, using a debug test system to manage the scan operation by employing Scan Selection Directives and unique addresses for each TAP controller.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If TAP controllers are connected in a star configuration for testing, then testing efficiency and accessibility are improved, but drive conflicts occur on shared signal lines during shift operations
Solution Approach 1:
The patent segments the shift operation by sequentially selecting individual TAP controllers to perform shift operations one at a time, while other TAP controllers remain in pause state. This segmentation of the previously concurrent shift operation eliminates drive conflicts on shared signal lines while maintaining the star configuration's testing efficiency benefits.
2Speed
If all TAP controllers perform shift operations concurrently in a star configuration, then testing speed is improved, but signal line conflicts arise
Solution Approach 1:
The patent implements periodic action by cycling through each TAP controller in sequence, allowing one controller to perform shift operations at a time while others pause. This periodic selection pattern maintains controlled testing speed while preventing simultaneous signal line conflicts that would occur with truly concurrent operations.
3Adaptability or versatility
If JTAG testing is performed on devices in a star configuration, then accessibility to multiple devices is improved, but the existing JTAG standard cannot support concurrent shift operations
Solution Approach 1:
The patent introduces dynamic state management where TAP controllers can transition between pause state and shift state based on selection signals. This dynamic behavior allows the system to adapt the operational mode of each TAP controller individually, enabling star configuration support while managing control complexity through standardized state transitions.
Data Source
AI summary
A method implemented to test a plurality of components coupled in a star configuration, each component having a test access port (TAP) controller. The method comprises performing a capture phase of a scan operation on all of the TAP controllers in the star configuration and sequentially selecting one of the TAP controllers at a time to perform a shift state. When all of the TAP controllers have been sequentially selected to perform the shift phase, the method further comprises selecting all of the TAP controllers to perform an update phase.